Known processes for biologically preparing lactic acid from DL-lactonitrile include a process of using a microorganism belonging to the genus Bacillus, Bacteridium, Micrococcus or Brevibacterium (see U.S. Pat. No. 3,940,316); a process of using a microorganism belonging to the genus Corynebacterium (see JP-A-61-56086, the term "JP-A" as used herein means an "unexamined published Japanese patent application"); a process of using a microorganism belonging to the genus Corynebacterium, Nocardia, Bacillus, Bacteridium, Micrococcus or Brevibacterium (see JP-A-61-162191); and a process of using a microorganism belonging to the genus Pseudomonas, Arthrobacter, Aspergillus, Penicillium, Cochliobolus or Fusarium (see JP-A-63-222696). Those processes relate to production of racemic lactic acid and not to production of an optically active lactic acid.
On the other hand, with respect to production of optically active hydroxy acids, there are known a process for producing an L-.alpha.-hydroxy acid which uses yeast of the genus Torulopsis (see JP-B-54-14668, the term "JP-B" as used herein means an "examined published Japanese patent application") and a process for producing an optically active .alpha.-substituted organic acid which uses a microorganism belonging to the genus Alcaligenes, Pseudomonas, Rhodopsuedomonas, Corynebacterium, Acinetobacter, Bacillus, Mycobacterium, Rhodococcus or Candida (see EP 0348901A). However, those processes do not make it possible to obtain a desired optically active compound in a predominant proportion from a starting racemate. Further, these are no illustrative examples concerning the preparation of an optically active lactic acid from DL-lactonitrile and thus, it is unclear whether an optically active lactic acid can be prepared with high efficiency and at a high optical purity by those processes.